Apparatuses for separating a mixture into solid material and liquid which make use of movable filtering means are known in the art. So-called horizontal belt filters and drum filters as well as so-called tilting pan or table filters are, for instance, known for specific applications, in particular for chemical processes, and washing processes are also carried out on movable filtering means, for instance, for washing out an acidic solvent from which plastic granules have formed.
Two types of apparatuses for separating into solid material and liquid a mixture thereof are commercially available. The first type is an apparatus provided with a reciprocally movable suction box disposed beneath an endless movable filter cloth. Here an extremely good seal is obtained between the suction box and the filter cloth so that the liquid is drawn out of the mixture with sufficient suction force. The second type relates to an apparatus provided with a belt of sealing material such as rubber moving along with the endless filter cloth.
In the above stated types of separating apparatuses, it is important to have the separation take place as efficiently and optimally as possible. Because the composition of the mixture can vary during the separating process, the quantity of liquid on the cake of solid material changes. At the beginning and end of separating steps, possibly different liquid may be mixed together. In practice, samples are usually taken from the solid material remaining behind on the movable filtering means in order to establish whether separating and/or washing has taken place to a sufficient extent.
European Patent Application EP-A-0316997 describes a method and system for monitoring and/or controlling a liquid solid separation process. The process describes use of four photo-detectors in a gravity dewatering zone of a belt filter press.
European Patent Application DE-A-4117682 describes controlling the speed of movement of filtering means which are moved from one roll to another, driven by a motor.
The present invention has for its object to optimalize the above stated separating process and separating apparatus, that is, to impose and maintain the quality standard requirements for the solid material and liquid for disposal.